Anytime you change an aspect of your suspension it is best to get an alignment. A slight difference in suspension geometry can affect your handling and your tire wear.
typically when you drop a car you get negative camber (which wears away at the inside of the tire). When this happens you add a little toe in on the rear (this allows for a slightly more even wear giving you more contact surface and longer tire life).
Mike
p.s. NTB has a 1 yr unlimited alignment plan. Works great if your making changes alot. I would always get it on my track going cars and switch back and forth all the time on setups.